1. Field of the Invention
The invention relates to an apparatus for the application of liquid adhesives to a substrate.
2. Description of the Prior Art
An apparatus can be used in conjunction with both hot melts and cold glues if adhesives have to be applied to screen print rotary cylinders or engraved printing rollers and also to flat substrates, for example textile materials.
German Offenlegungsschrift No. 3,248,889 discloses an apparatus for the application of surface coatings to a textile substrate which comprises a nozzle-shaped mouth gap of a bar-shaped coating head which is subjected to pressure. In front of the coating head a perforated metal cylinder rotates as a template. The coating head contains a cavity and a chamber mouth which is defined by two sealing lips and is sealed laterally by a profile bar introduced on each of the two sides and having the same cross-section as the chamber mouth. The width of chamber mouth can be adjusted by using profile bars of various lengths or by displacing the profile bars.
U.S. patent application Ser. No. 937,859 discloses an apparatus for the intermittent application of liquids, such as adhesives, in particular hot melts, to a substrate moved relatively to the apparatus, in which upstream of the nozzle, a needle valve is provided for interrupting the flow from a supply container to the nozzle at desired intervals; Adjoining the supply conduit, in front of the main valve, is a return conduit to the supply container. In the return conduit, a second needle valve is disposed for shutting off the return conduit.
The second needle valve is larger than the main valve and is a pre-valve in the supply conduit at a short distance upstream of the main valve. The valves can be controlled in an adjustable time relationship with respect to each other so that even at high frequencies, an optimum application of the adhesive is achieved. In particular at the start and end of the application.
Finally, an apparatus for the application of liquid adhesives of the type set forth is apparent from German patent specification No. 3,541,784. The apparatus comprises a supply container and an applicator nozzle for the adhesive as well as a shut-off valve in the conduit from the supply container to the nozzle. The nozzle is formed as slit nozzle having a slit emanating from a spreading chamber. The adhesive is supplied to the spreading chamber by a passage which opens centrally into the spreading chamber at an angle to the direction in which the slit adjoins the chamber. The chamber extends substantially on one side of the slit. To ensure optimum distribution of the adhesive over the entire width of the slit with a simple nozzle structure, the passage opens into the chamber from the other side of the slit.
The problem with all the conventional applicator apparatuses is that of obtaining a uniform adhesive layer on the substrate to be coated, taking into account, on the one hand, various layer thicknesses and on the other hand, the highly fluctuating viscosities of the adhesives to be applied.
In particular, it has not hitherto been possible to readjust the applicator nozzle rapidly for different layer thicknesses and/or viscosities of the adhesive.